Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece, wafer, or substrate, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned, etched, or altered to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
Many ICs include electrostatic discharge (ESD) protection circuits designed to protect the ICs against transient voltages such as ESD events and surges. An ESD protection circuit typically is designed to turn on during an ESD event and form a current discharge path to shunt the large ESD current and clamp the voltage of input/output (I/O) and supply pads to a sufficiently low level to prevent the IC from being damaged. The current shunting path is often provided by an active device that provides a conduction path with a relatively low on-resistance, for example. The ESD protection circuit typically ensures a low resistance path to prevent voltages from building up to potentially damaging levels.
ESD protection circuits may include elements such as diodes, resistors, thyristors, transistors, and/or capacitors, as examples. Some ESD protection circuits may include a trigger circuit, a buffer circuit, and/or a clamping circuit, as examples.
However, area on integrated circuits (ICs) is often limited. Further, as some devices on ICs, such as logic circuitry, memory, and other circuitry are scaled to smaller geometries, the size of ESD protection circuits may not necessarily decrease in size. ESD protection circuits may occupy a large percentage of the surface area of a die and may limit further reduction in size of an IC and increase cost.
Further, as operational frequencies increase, parasitic capacitances on input and output connections become more significant. Thus, improved ESD protection circuits are needed which occupy small IC areas and include minimal parasitic capacitances.